A) Field of the Invention
This invention relates to a solid state imaging apparatus and more specifically to a driving method of a solid state imaging apparatus.
B) Description of the Related Art
FIG. 5 is a schematic plan view of a conventional solid state imaging apparatus 51.
The solid state imaging apparatus 51 is consisted of a light receiving region 52 including a multiplicity of photo electric conversion elements 52 and vertical electric charge transfer devices (vertical charge coupled devices: VCCD) 64 for transferring electric charges generated in the photo electric conversion elements in a vertical direction, a horizontal electric charge transfer device (horizontal charge coupled device: HCCD) 73, and an output amplifier 74.
The light receiving region 64 of the imaging device to which a pixel interleaved array CCD (PIACCD) is applied as shown in the drawing has the multiplicity of the photo electric conversion elements 52 arranged in so-called pixel interleaved arrangement. Between columns of the photo electric conversion elements 54, the vertical electric charge transfer device 64 that reads out electric charges generated in the photo electric conversion elements 54 and transfers them in the vertical direction is placed by sewing spaces between the photo electric conversion elements to the vertical direction. Winding transfer channels are formed in spaces formed by the pixel interleaved arrangement, and adjacent transfer channels are going away from each other via the photo electric conversion element 52 and coming closer to each other via a channel stop region 53. For example, the details of the pixel interleaved arrangement can be found in Japanese Laid-Open Patent Hei10-136391 and Tetsuo Yamada, et al, February, 2000, “A Progressive Scan CCD Imager for DSC Applications”, ISSCC Digest of Technical Papers, Page 110 to 111.
The vertical electric charge transfer device 64 is consisted of the vertical transfer channel 54 shown in FIGS. 6A and in 6B and transfer electrodes 16a and 16b which are formed over the vertical transfer channel 54 via an insulating film 10a and wobbling the photo electric conversion elements 52 to the horizontal direction.
FIG. 6A is an enlarged plan view showing a part of the light receiving region 52 in the conventional solid-state imaging apparatus 51. FIG. 6B is an enlarged cross sectional view showing the conventional solid-state imaging apparatus 51 cut across a broken line A-B in FIG. 6A.
Each of the vertical transfer channel 54 is formed corresponding to each row of the photo electric conversion elements 52, and transfers the signal electric charges read out via a reading-out gate channel region 51c formed adjoining to each photo electric conversion element 52 to the vertical direction. A channel stop region 53 is positioned adjoining to the vertical transfer channel 54 on the opposite side of the reading-out gate channel region 51c. Moreover, the transfer electrodes 56 (the first layer poly-silicon electrode 56a and the second layer poly-silicon 56b) are formed over the vertical transfer channel 54 via the insulating film 60a. Furthermore, at the cross section of this part, only the second layer poly-silicon electrode 56b is positioned over the vertical transfer channel 54. Further, the conventional solid-state imaging apparatus 51 has a structure wherein the two vertical transfer channels 54 are adjoining via the channel stop regions 53.
During a reading-out period, the signal charges generated by the photo electric conversion elements (pixel) 52 are read out to the vertical transfer channels by impressing a high level voltage (VH) to the first layer poly-silicon electrode 56b (φV1) or 56d (φV3) equipped on the reading-out gate channel region (reading-out part) 51c. 
Thereafter, during a transfer period, the signal charges are transferred to the HCCD 73 by sequentially impressing a mid-level pulse (VM) or a low-level pulse (VL) to the transfer electrodes 56a to 56d. A horizontal transfer of the electric charges by the HCCD 73 is executed by the two-phase drive with HM/HL pulses during a period between the transfer operations of the VCCD 64 in the transfer period.
FIG. 7 shows electric potentials between a broken line E-F in FIG. 6B. An overflow drain that discharges an excessive signal electric charge of the photo electric conversion elements 52 is formed by adding an inverse bias on an n-type substrate 51a to form an appropriate electric potential barrier between the photo electric conversion element 52 and the n-type substrate 51a. 
In the drawing, the electric potential indicated with a solid line is in a condition that the electric charges are accumulated in the photo electric conversion element 52. Since a low voltage (VM or VL) is impressed on the electrode 56b, a reading part 51c is closed, and the accumulated signal charges are not read out to the vertical transfer channel 54.
In the drawing, the electric potential indicated with a dashed line is in a condition that a high voltage (VH) is impressed on the electrode 56b, and the electric potential barrier to the vertical transfer channel 54 from the photo electric conversion elements 52 is eliminated by impressing a sufficient high voltage, and all the electric charges will move to the vertical transfer channel 54. Moreover, two vertical transfer channels 54 which are adjacent via the channel stop region 53 become high electric potential, although the channel stop region 53 divides them. Since the signal electric charges are accumulated in the vertical transfer channel 54 which is adjacent to the reading part 51c at the reading-out period, the signal charges that can be accumulated in the vertical channel 54 in terms of electric potential will not exceed the electric potential of the channel stop region 53.
FIG. 8 is an enlarged plan view showing a part enclosed with a double short-dashed line in FIG. 6A. In the drawing, S2 indicates a region of a channel formed by the electrode 56b at the reading-out period. An accumulation capacity at the reading-out period is decided approximately by a difference φa between the electric potential of the vertical transfer channel 54 that is adjoining to the reading part 51c shown in FIG. 7 and the electric potential barrier of the channel stop region 53 and an area of the S2 and a static capacity for the area per unit (the maximum accumulation capacity equals to or approximately equals to αS2φa, when α is the static capacity for the area per unit).
In a case that this maximum accumulation capacity is smaller than the maximum accumulation capacity of the photo electric conversion element 52, the signal electric charges flow into an adjacent vertical transfer channel 54m over the electric potential barrier of the channel stop region 53, and it causes a blooming phenomenon that will deteriorate an image of a blight part as the solid-state imaging apparatus. That is, the dynamic range will be lost as a reduction of the dealing signal amount.
FIG. 9A to FIG. 9C are diagrams for explaining a conventional driving method of all pixel reading when electric charges are read out from the photo electric conversion elements 52 to the vertical transfer channel 54. In the drawing, a white circle represent an electric charge, and each electric charge corresponds to one of colors represented by letters “R, G, B” placed inside the circle. Moreover, a black painted part of the vertical transfer channel shows a state of a high electric potential when the black painted part can accumulate electric charges.
FIG. 9A shows an initial condition, each photo electric conversion element 52 accumulates electric signal charge corresponding either one of “R, G, B”. From the initial condition, the electric charges (G signals) stored in the photo electric conversion elements 52 are read out to the vertical transfer channel 54 by impressing high level voltage (VH) to φV1 as shown in FIG. 9B. At this time, the electric charges may flow into adjacent vertical transfer channel 54 over a potential barrier of the channel stop region 53. Thereafter, the electric charges (R signals and B signals) stored in the photo electric conversion elements 52 are read out to the vertical transfer channel 54 by impressing high level voltage (VH) to φV3 as shown in FIG. 9C. At this time also, the electric charges may flow into adjacent vertical transfer channel 54 over a potential barrier of the channel stop region 53. Therefore, this inter-VCCD blooming phenomenon causes color mixture and, as a result of that, an image in a light part will be extremely deteriorated.